Update GettingStarted with link to prebuilt images
Update GettingStarted with link to prebuilt images

Update prebuilt images usage instructions

Show how to register the prebuilt image with glance

Change-Id: I27d032644dc7062a9cb5c88ed95c08ed146a3665

jasondunsmore/heat,noironetworks/heat,miguelgrinberg/heat,redhat-openstack/heat,Triv90/Heat,dragorosson/heat,pratikmallya/heat,varunarya10/heat,rickerc/heat_audit,rdo-management/heat,Triv90/Heat,ntt-sic/heat,redhat-openstack/heat,jasondunsmore/heat,dragorosson/heat,srznew/heat,cwolferh/heat-scratch,maestro-hybrid-cloud/heat,cwolferh/heat-scratch,rh-s/heat,NeCTAR-RC/heat,rh-s/heat,NeCTAR-RC/heat,noironetworks/heat,pshchelo/heat,dims/heat,rickerc/heat_audit,openstack/heat,citrix-openstack-build/heat,miguelgrinberg/heat,JioCloud/heat,pratikmallya/heat,pshchelo/heat,takeshineshiro/heat,varunarya10/heat,gonzolino/heat,steveb/heat,cryptickp/heat,cryptickp/heat,srznew/heat,openstack/heat,rdo-management/heat,maestro-hybrid-cloud/heat,ntt-sic/heat,JioCloud/heat,citrix-openstack-build/heat,gonzolino/heat,dims/heat,steveb/heat,takeshineshiro/heat,Triv90/Heat